What type of controller is referred to in the statement <apex:page controller="AccountController">?

The statement <apex:page controller="AccountController"> refers to a Custom Controller. This is because it specifies a controller class (in this case, "AccountController") that is defined by the developer. A custom controller is an Apex class that directly supports the Visualforce page and contains its own logic and methods, allowing for greater control over the behavior of the page.

In contrast, a standard controller would automatically provide the basic CRUD (Create, Read, Update, Delete) functionality for standard objects without any custom logic. A controller extension would be used to extend the functionality of an existing standard or custom controller, enabling the integration of additional features or methods while still relying on the behaviors provided by the extended controller. The term specific controller is not commonly used within the context of Salesforce, making it less relevant compared to the other terms.

The use of a custom controller this way provides flexibility for developers to implement specific business logic or custom behavior that cannot be achieved with standard controllers or controller extensions.